Light-emitting diodes (LEDs) are semiconductors that are widely used in light sources. Comparing to conventional tungsten lamps or cold cathode fluorescent lamps (CCFLs), LEDs consume less power and have longer lifetime. Therefore, LEDs are replacing the conventional light sources gradually, and utilized in various fields. For example, the LEDs are capable of being employed in traffic lights, optical display devices, data storage devices, communication devices, illuminative equipments and medical equipments. The desire of brightness of the LEDs increases as the usage and development of the LEDs evolves, thus one of the main goals of engineers who design LEDs is to increase the brightness of the LEDs.
One method for enhancing brightness and luminous flux of LEDs is to enlarge surface area of a chip. However, when the surface area of the chip is enlarged, an electric current can not be spread uniformly from a contact electrode into a light-emitting layer; and if the surface area of the contact electrode is enlarged to make the electric current spread uniformly, an effect of light blocking would occur and thus the light extraction is reduced. In this regard, how to spread the electric current uniformly in the light-emitting layer and increase the brightness of the LED without changing the surface area of the contact electrode is a problem need to be solved.
A conventional method for spreading the electric current is performed by using a semi-transparent current spreading layer formed on a p-type semiconductor layer. Generally, for reducing effect of absorbing light, it is preferred to have a thinner semi-transparent current spreading layer. However, the thinner the semi-transparent current spreading layer is, the higher its sheet resistance is.
What is needed, therefore, is a semiconductor device that can overcome the above-mentioned shortcomings.